效果图：
代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Generate Random Four-Digit Verification Code</title>
</head>
<body>
<h1>点击生成四位随机数</h1>
<input type="text" id="verificationInput">
<button id="generateCode">Generate Code</button>
<script>
const generateCodeButton = document.getElementById("generateCode");
const verificationInput = document.getElementById("verificationInput");
let randomCode = '';
generateCodeButton.addEventListener('click', function() {
randomCode = Math.floor(1000 + Math.random() * 9000); // Generate a random four-digit number
verificationInput.value = randomCode;
});
verificationInput.addEventListener('click', function() {
verificationInput.value = randomCode;
});
</script>
</body>
</html>当前效果是需要点击按钮，也可以写在点击按钮里面，根据需求适当调整；
希望可以帮到你们；